Gate valves, such as the one shown in Crain et al, U.S. Pat. No. 3,349,789, issued Oct. 31, 1967 often and necessarily are provided with seals and packing that works well, lasts long and maintains its integrity under ordinary circumstances, but which is subject to being damaged should there be a fire the heat of which engulfs the valve for more than a short period of time. Accordingly, proposals have been made for providing such valves with a second line of defense, which comes into play only if a fire or the like should threaten to or actually destroys the integrity of the usual seals and packing. A typical environment where such a precaution is worthwhile taking is where the valve is to be used to control the egress of subterranean fluids (i.e. as part of a petroleum well completion). Other typical environments for use are petroleum refineries, petrochemical complexes, and chemical manufacturing, processing, storage, handling, transportation and use facilities.
According to some prior art proposals, the valve is provided with one or more fusible bodies which, when in place, keep the back seat elements apart. Upon subjection of the valve to sufficient heat, the fusible body or bodies flow out, permitting some crucial shifting of the valve components that cause a metal back seat seal to be made up, providing a measure of additional safety.
What the present invention provides is a convenient way to provide the fusible body or bodies on valves of the type described and for similar apparatus.